GB1570330A - Powerassisted rack-and-pinion steering mechanism for motor vehicles - Google Patents

Description

(54) POWER-ASSISTED RACK-AND-PINION STEERING MECHANISM FOR MOTOR VEHICLES (71) We, BENDIBERICA S.A., of 243 Balmes, Barcelona 6, Spain, a Spanish Body Corporate, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following state ment:- The invention relates to a power-assisted rack-and-pinion steering mechanism for motor vehicles.

It has already been proposed that in a motor vehicle with one set of direction-controlling wheels the steering of the wheels should be controlled by a rack steering mechanism in which a rack meshes with a pinion, the pinion being rotated by the steering column by way of a rotary hydraulic power assisting valve connected to the direction-controlling wheel set and able to cooperate with the rack in order to cause the wheels to turn.

When the vehicle has a plurality of sets of direction-controlling wheels, the use of power-assisted rack-and-pinion steering mechanism of this type for each set of direction-controlling wheels requires mechanically and hydraulically synchronised operation of the racks.

The invention therefore consists of a power-assisted rack-and-pinion steering mechanism in a motor vehicle comprising two racks, of which each is coupled to a set of direction controlling wheels in the vehicle and each meshes with a opinion, the pinions being rotationally connected to a rotatable casing of a torque responsive power steering valve which senses the magnitude and sense of direction of the torque in a steering column and communicates pressure fluid from a source and reservoir pressure to respective chambers of each ram associated with a respective rack, so as to provide each set of direction controlling wheels with hydraulic power assistance synchronized with the rotation of its corresponding pinion, the pinion for each rack being situated substantially on the axis of the rotatable casing of the power steering valve, wherein a torque limiting mechanism is situated in a shaft between the two pinions, the said torque limiting mechanism being operative to mechanically desynchronize the two pinions when the torque in said shaft exceeds a predetermined thres- hold.

The invention will be better understood from the ensuing description referring to the accompanying drawings, in which:.

Figure 1 is a simplified diagråm - of a vehicle comprising power-assisted rackand-pinion steering mechanism embodying the invention; Figure 2 represents a section through the power-assisted rack-and-pinion steering embodying the invention, with a first main power steering system and a second- auxiliary power steering system; Figure 3 shows the rotary valve from Figure 2 on a larger scale; Figure 4 is a cross-section along a line 3-3 through the rotary valve shown in Figure 2, in the idle position; Figure 5 is a cross-section along the line 3-3 through the rotary valve shown in Figure 2, in the operative position; Figure 6 is a section through a- torque limiting device used in the system shown in Figure 1; Figure 7 is a section along a line 7-7 through the torque limiting device shown in Figure 6; Figure 8 is a developed section along a line 8-8 in Figure 7; Figure 9 is a section along a line 9-9 in Figure 8; and Figure 10 is a section through a variant of the device shown in Figure 6.

Figure I shows a steering wheel 10 which operates a power-assisted rack-and-pinion steering system 12 by way of a bevel gear 14. At each end of the piston rod of the power steering a swivel joint 16 cooperates with a link 18 and rod 20 to transmit the controlling movement to the front direction-controlling wheels. At the opposite end from the extension of the input shaft 22 associated with the torsion bar of a rotary power steering valve, there is an output shaft 24, which is rotationally connected to the shaft 22 and whose role will be described below. A hydraulic pump 26 operated by the engine of the vehicle and supplied with oil from a reservoir 28 supplies the high pressure to the inlet orifice or port of the power steering valve, the outlet orifice or port of the valve being connected to the reservoir 28. Steering of the rear direction-controlling wheels is effected by means of an auxiliary power-assisted rackand-pinion steering system 30, which is of a similar type to that for the front wheels and of which like elements bear like reference numerals. This second power steering system does not have its own control valve, and the fluid supply to the rams in the front and rear power steering systems is controlled from the single valve mentioned above. The auxiliary power steering system is supplied with fluid along pipes 32, 34. The input shaft 36 of the power steering system 30 cooperates with the output shaft 24 by way of transmission means which is generally designated 38, and which comprises a torque limiting device 40 whose role is stated below.

Figure 2 represents a cross-section through a power-assisted rack-and-pinion steering mechanism embodying the invention, with a main rack-and-pinion power steering system 12 and an auxiliary rackand-pinion power steering system 30 and cooperating with the front and rear direction-controlling wheels respectively. In Figure 2, in which like elements bear the same reference numerals as in Figure 1, a conventional rotary power steering valve is designated 50. The rotary valve comprises, in a known manner, an input shaft 22 collected at one end to the rotor 52 of the valve. It also has a torsion bar 54 of which one end is fixed to the input shaft, a housing 56 and a sleeve 58 situated between the housing and rotor. The sleeve 58 is attached to the output shaft 24 and to a pinion 60 provided on the output shaft. The pinion 60 meshes with a rack 62 belonging to the main power steering system associated with the front wheels. The rack 62 can move inside two coaxial tubes 64, 66 of identical diameters, these being arranged to define a bore closed at both ends. The rack 62, which is of a known type, has a plug 63, 65 at each end, these plugs being slidable in a fluid-tight manner in the respective tubes 64, 66 so as to define, between each closed end of the bore and the corresponding plug, the chambers 68, 70 of a hydraulic power-assisting ram. The central part of the bore is enclosed by an intermediate member 72 which connects the tubes 64, 66 to the rotary valve. At the intermediate member, the bore is traversed at right-angles to its axis by the output shaft 24 of the rotary valve 50, of which the pinion 60 meshes with the rack 62. The housing 56 contains an intake orifice 74 connected to the delivery side of the pump 26 and a discharge orifice 76 connected to the reservoir 28. The housing also contains two work orifices 78, 80 whose roles will be described below. Note that the work orifice 80 is permanently connected to the chamber 70 by a pipe 82 and by an orifice 84 formed in the wall of the bore of the chamber 70. Similarly, the working orifice 78 communicates with the chamber 68 via a passage 98 in the power steering valve, via the central part of the bore and via a passage 73 connecting this central part to the chamber 68. A second rack-and-pinion power steering system 30, termed the auxiliary steering system, is associated with the rear wheels as shown in Figure 1. It is identical to the main power steering system associated with the front wheels. The input shaft 36 is associated with the output shaft 24 of the main power steering in the manner illustrated in Figure 1. The other components of the auxiliary power steering system bear the same reference numerals as those in the main power steering system plus 100. The chamber 168 is connected to the work orifice 78 by the pipe 32, and the chamber 170 is connected to the work orifice 80 by the pipe 34.

The rotary power steering valve is of a conventional type. As already stated, it has a rotor 52 and a sleeve 58. The rotor contains six axial grooves equispaced round its periphery. As best shown in Figure 3, these grooves are made up of a first group of three long grooves 92 and a second group of three shorter grooves 93, with grooves 92 and 93 alternating around the periphery of the rotor.

The sleeve contains three radial orifices 90 (Figure 4) equispaced round its periphery and communicating with the delivery port of the hydraulic pump. Between each of its orifice 90 the sleeve contains radial orifices 94, 96 communicating with the respective work orifices of the power steering valve. The radial orifices 94, 96 end in grooves formed in the inner periphery of the sleeve and are intended to supply the chambers of the power rams with different hydraulic pressures in response to the application of stress to the rotor of the power steering valve for the purpose of operating the power ram.

The operation of the steering mechanism described above will be better understood by referring, in addition to Figures 2 and 3, to Figures 4 and 5, which represent sections along the line 3-3 through the rotary valve shown in Figure 2 in the idle and operative positions respectively.

In the idle position shown in Figure 4, 52 designates the valve rotor attached to the input shaft 22, and 58 designates the valve sleeve attached to the output shaft 24 and pinion 60. In this idle position oil is fed from the pump 26 along a pipe 37 to the inlet orifice 74 and passes through the on fices 90 in the sleeve 58. The oil then flows unrestricted to the grooves 92 in the rotor 52 along the grooves 93 in the rotor and the grooves in the sleeve 58, the grooves 92 communicating permanently with the reservoir 28 by way of the discharge orifice 76 and a pipe 39. There is no power assistance since the pressure in the orifices 90 is very similar to that in the reservoir, and the pressures supplied at the work orifices of the rotary valve are also substantially identical to the reservoir pressure.

Figure 5 shows the valve 50 in the operative postiion, when the valve is operated clockwise. In this case, a restriction has been produced between the orifices 90 and the grooves 92, more particularly between the grooves 93 and the sleeve grooves associated with the orifices 94, which causes a pressure rise in the orifices 90. This relatively high hydraulic pressure is transmitted through the orifices 96, along the passage 98 in the body of the rotary valve and along the central bore formed by the tubes 64, 66 to the passage 73 and so into the chamber 68 of the main power steering system; also, the relatively high pressure is transmitted through the outlet orifice 78 and pipe 32 to the chamber 168 of the auxiliary power steering. The grooves 92 in the rotor which are permanently connected to the discharge pipe 39 are connected to the chambers 70, 170 of the main and auxiliary power steering systems respectively by way of the orifices 94 communicating with the external pipes 82 and 34. This gives synchronised hydraulic and mechanical operation of the direction-controlling wheels. If the input shaft is operated anticlockwise, the chambers and pipes which were connected to the high pressure in the previous case will remain connected to the discharge orifice, and vice versa.

During normal operation, the shafts 24, 36 of the main and auxiliary power steering systems are rotated synchronously and are connected by the transmission means 38. The transmission means 38 includes the torque limiting mechanism 40, since the latter may be exposed to torsional stresses caused by transfers of stresses from one direction to the other, for example due to different ground adhesion of the wheels on the different axles owing to uneven load distribution between the axles, or due to irregularities in the ground. This transfer may also take place when operation is purely manual, in which case the stress transmitted to the auxiliary steering travels from the steering wheel by way of the main steering and the transmission means 38. Although the transmission is designed to withstand relatively large transfers of stress, it may happen that the stress becomes great enough to damage the mechanism. - To overcome this disadvantage, the torque limiting mechanism 40 inserted in the transmission means 38 (Figure 1) permits the two steering systems to be desynchronised immediately after the permitted stress transmission limit is reached. Synchromsa- tion of the two systems is re-established automatically when the stresses return below this threshold.

Figure 6 represents a section through one embodiment of torque limiting device used in the ssytem shown in Figure 1.

The shafts 24, 36 are coaxial, and each of the mutually facing ends supports a collar 210, 212 rotationally connected to their respective shafts by means of splines. The mutually facing annular sides of the collars 210, 212 contain identical grooves 214 which face one another and whose longitudinal axes are arcuate. Balls 216 are gripped between the grooves 214 and normally transmit the torque between the two shafts.

In the embodiment shown in Figures 6 and 7, each collar contains three grooves, but this number can be changed according to the designer's wishes.

The other side of each collar 210, 212 supports one end of a respective spring 218 or 219, the springs being coaxial with the shafts 24 and 36 respectively. The other end of the spring 218 bears on adjustable locking means consisting of a nut 220 and a locknut 222, both screwed on to a threaded portion of the shaft 24. Similarly, the other end of the spring 219 bears on identical locking means 224, 226 provided on the shaft 36.

Figure 8 illustrates the longitudinal profile of the groove in its central part. This profile is in two parts which have substantially identical gradients and which join at the centre to define the deepest part of the groove. When the torque limiting device is in its idle position, the balls 216 are in the middle of the groove, which is also the deepest part.

Figure 9 represents a section along a line 9-9 in Figure 8 and shows how the crosssection of the groove 214 is substantially rounded, in the form of a circular arc.

The torque limiting device just described operates as follows. When the torque exerted on the balls 216 is less than a predetermined value, the force which is exerted on each ball 216, and which equals the resultant of the force of the spring and of the force created by the torque, is insufficient to move the balls 216 out of their central position, in view of the resistance offered by the slope in the groove 214. The two shafts are now coupled.

When the torque exceeds the predetermined value, the balls 216 can slide along the grooves, causing relative rotation of the shafts 24, 36 through an angle determined by the length and gradient of the grooves.

During this rotation, the shafts 24, 36 are uncoupled.

The torque limiting device just described must be able to operate in the event of rotation of the rotor, that is, of the pinion, corresponding to the entire stroke of the ram piston.

The torque limiting device must therefore permit uncoupling of the shafts 24, 36 at an angle of relative rotation up to a maximum predetermined level in response to the application of a torque greater than the limiting torque. In general, the combination of only two collars as shown in Figure 6 will not achieve this result. In such cases, it is preferable to use a variant like that illustrated in Figure 10, with a larger number of collars and balls interposed between the collars, since this allows the angle of deviation to be increased.

WHAT WE CLAIM IS: 1. A power-assisted rack-and-pinion steering mechanism in a motor vehicle comprising two racks, of which each is coupled to a set of direction controlling wheels in the vehicle and each meshes with a pinion, the pinions being rotationally connected to a rotatable casing of a torque responsive power steering valve which senses the magnitude and sense of direction of the torque in a steering column and communicates pressure fluid from a source and reservoir pressure to respective chambers of each ram associated with a respective rack, so as to provide each set of direction controlling wheels with hydraulic power assistance synchronized with the rotation of its corresponding pinion, the pinion for each rack being situated substantially on the axis of the rotatable casing of the power steering valve, wherein a torque limiting mechanism is situated in a shaft between the two pinions, the said torque limiting mechanism being operative to mechanically desynchronize the two pinions when the torque in said shaft exceeds a predetermined threshold.

2. A power-assisted rack-and-pinion steering system substantially as hereinabove described and as illustrated in the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. force created by the torque, is insufficient to move the balls 216 out of their central position, in view of the resistance offered by the slope in the groove 214. The two shafts are now coupled. When the torque exceeds the predetermined value, the balls 216 can slide along the grooves, causing relative rotation of the shafts 24, 36 through an angle determined by the length and gradient of the grooves. During this rotation, the shafts 24, 36 are uncoupled. The torque limiting device just described must be able to operate in the event of rotation of the rotor, that is, of the pinion, corresponding to the entire stroke of the ram piston. The torque limiting device must therefore permit uncoupling of the shafts 24, 36 at an angle of relative rotation up to a maximum predetermined level in response to the application of a torque greater than the limiting torque. In general, the combination of only two collars as shown in Figure 6 will not achieve this result. In such cases, it is preferable to use a variant like that illustrated in Figure 10, with a larger number of collars and balls interposed between the collars, since this allows the angle of deviation to be increased. WHAT WE CLAIM IS:

1. A power-assisted rack-and-pinion steering mechanism in a motor vehicle comprising two racks, of which each is coupled to a set of direction controlling wheels in the vehicle and each meshes with a pinion, the pinions being rotationally connected to a rotatable casing of a torque responsive power steering valve which senses the magnitude and sense of direction of the torque in a steering column and communicates pressure fluid from a source and reservoir pressure to respective chambers of each ram associated with a respective rack, so as to provide each set of direction controlling wheels with hydraulic power assistance synchronized with the rotation of its corresponding pinion, the pinion for each rack being situated substantially on the axis of the rotatable casing of the power steering valve, wherein a torque limiting mechanism is situated in a shaft between the two pinions, the said torque limiting mechanism being operative to mechanically desynchronize the two pinions when the torque in said shaft exceeds a predetermined threshold.

2. A power-assisted rack-and-pinion steering system substantially as hereinabove described and as illustrated in the accompanying drawings.